The present invention relates to a method for forming a wire.
A method for forming a wire having a dual damascene structure, which is one of wire forming methods, is as follows: After a via hole and a wiring groove (hereinafter also referred to as a trench) are formed by patterning an insulating film, a wire is formed by burying a conductive film in the hole and groove. There are cases where a film composed of a material having a dielectric constant lower than that of the silicon oxide film (i.e., a low dielectric constant film), such as a silicon oxide film containing an organic material (i.e., a carbon-containing silicon oxide film), or a porous film is used as the insulating film between wires such that a wire-to-wire capacitance is reduced.
In a conventional wire forming method disclosed in Japanese Laid-Open Patent Publication No. HEI 11-243147, a dual damascene structure is formed by forming a via hole in a carbon-containing silicon oxide film and etching the carbon-containing silicon oxide film by using a resist film having a trench pattern as a mask.
In a conventional wire forming method using a low dielectric constant film such as a carbon-containing silicon oxide film, however, the problem is encountered that, if a trench pattern is to be formed by lithography using a chemically amplified resist, a resist film having a desired trench pattern cannot be formed. The problem will be described specifically with reference to the drawings.
FIGS. 10A and 10B show the problem encountered when a chemically amplified positive resist is used in the conventional wire forming method. As shown in FIG. 10A, an insulating film 52 in which a first wire 53 is buried is formed on a substrate 51. A protective film 54, an organic-material-containing silicon oxide film 55, and an antireflection film 56 are formed successively over the insulating film 52 including the first wire 53. After a via hole 57 was formed in the organic-material-containing silicon oxide film 55 and in the antireflection film 56, when a resist film 58 having a trench pattern was to be formed on the antireflection film 56 by lithography using a chemically amplified positive resist, the following problem occurred. When development was performed after the irradiation of the resist film 58 with light, the portion of the resist film 58 located in a trench formation region was not sufficiently dissolved so that a post-develop defect F, specifically the trailing of the resist (the remaining of the resist in a trailing fashion even in the hole), occurred. When the antireflection film 56 and the organic-material-containing silicon oxide film 55 were etched by using, as a mask, the resist film 58 including the trailing portion, a trench 59 having a fence 60 is formed, as shown in FIG. 10B. Due to the fence 60, the connection resistance between a wiring portion formed in the trench 59 and a plug portion formed in the via hole 57 is increased disadvantageously.
FIGS. 11A and 11B show a problem encountered when a chemically amplified negative resist is used in the conventional wire forming method. As shown in FIG. 11A, the insulating film 52 in which the first wire 53 is buried is formed on the substrate 51. The protective film 54, the organic-material-containing silicon oxide film 55, and the antireflection film 56 are formed successively over the insulating film 52 including the first wire 53. After the via hole 57 was formed in the organic-material-containing silicon oxide film 55 and in the antireflection film 56, when the resist film 58 having a trench pattern was to be formed on the antireflection film 56 by lithography using a chemically amplified negative resist, the following problem occurred. When development was performed after the irradiation of the resist film 58 with light, the resist film 58 was dissolved in a range wider than a trench formation region as desired. In other words, the resist film 58 having a trench pattern larger than a desired mask size was formed. When the antireflection film 56 and the organic-material-containing film 55 were etched subsequently by using the resist film 58 as a mask, the trench 59 having dimensions different from desired ones was formed disadvantageously, as shown in FIG. 11B.
FIG. 12A is a plan view showing a resist film having a trench pattern with desired mask dimensions which has been formed on an insulating film formed with a via hole.
By contrast, FIG. 12B is a plan view showing a resist film having a trench pattern with a trailing portion which has been formed by lithography using a chemically amplified positive resist on an insulating film formed with a via hole. As shown in FIG. 12B, there are cases where the connecting portion between the via and the trench is narrowed. In lithography using a positive resist, the resist irradiated with light is normally removed by development. In the case shown in FIG. 12B, however, the portion of the resist adjacent the via hole is not sufficiently removed so that the trench pattern with the trailing portion is formed disadvantageously.
On the other hand, FIG. 12C is a plan view showing a resist film having a trench pattern larger than desired mask dimensions which has been formed by lithography using a chemically amplified negative resist on an insulating film formed with a via hole. If the width of the trench pattern is increased, as shown in FIG. 12C, adjacent trenches may be combined with each other to cause a wiring short circuit. In lithography using a negative resist, the resist irradiated with light normally remains without being removed by development. In the case shown in FIG. 12C, however, the portion of the resist adjacent the via hole is removed upon development so that a trench pattern having an increased width is formed disadvantageously.